Considering the draconian prime directive interpretation of the 24th century, the federation integrating new members (aka interfering) is practically a plot hole:

Preparing cultures for membership in the federation by trying to steer their values (by cultural exchange) - blatant violation of the prime directive!
A society enters the federation when all its members ask for membeership? No society has only one opinion - there are many voices. And majority opinion is not enough to justify federation interference (as proven in the klingon civil war).
Giving new members technology more advanced than their own - blasphemy!

Letting species die rather than interfere because...if you interfere the entire species will commit suicide? Ridiculous! During our entire history, there is NO SINGLE CASE in which a society was 'overwhelmed' and commited mass suicide, regardless of what it was confronted with.

Hell - it's a wonder the federation actually explores (interfering!) and doesn't stay at home, hidden under cloacking fields - just to make sure no other people will see it and be influenced by the federation and its values!